This application is a 35 USC 371 application of PCT/DE 00/02820 filed on Aug. 8, 2000.
1. Field of the Invention
The invention relates to a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a plurality of connection openings, in particular connection openings for delivering and removing fuel and connection openings for sensors and valves and so forth.
2. Description of the Prior Art
In common rail injection systems for internal combustion engines, a high-pressure pump, optionally with the aid of a prefeed pump, pumps the fuel to be injected out of a tank into the central high-pressure fuel reservoir, which is called a common rail. From the rail, high-pressure lines lead to the individual injectors that are assigned one to each of the engine cylinders. The injectors are triggered individually by the engine electronics as a function of the operating parameters of the internal combustion engine, in order to inject fuel into the combustion chamber of the engine. By means of the high-pressure fuel reservoir, the pressure generation and the injection are decoupled from another.
A conventional high-pressure fuel reservoir is described in German Patent Disclosure DE 196 40 480, for instance. The known high-pressure fuel reservoir comprises an elongated, tubular body with a plurality of connections for supplying fuel injection valves, which are also called injectors. The tubular body has the simultaneous functions of pulsation damping over its volume and of distributing the fuel via the connections. Depending on the adaptation in the system, pressure pulsations occur, especially when the inside diameter of the tube is small and the length of the tube is great. The pressure pulsations mean that some injectors will inject too little, because of the development of a standing pressure wave. Pressure waves running back and forth in the rail can also mean that the injectors either in alternation or stochastically inject an overly small fuel quantity. To damp the pulsations in the rail, a relatively large volume is needed. The large volume makes it more difficult and expensive to design the rail to withstand high pressure.
The object of the invention is to furnish a high-pressure fuel reservoir of the type defined at the outset that has greater strength and a longer service than conventional high-pressure fuel reservoirs. Nevertheless, the high-pressure fuel reservoir of the invention should be simple in design, and it should be possible to produce it economically.
In a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a plurality of connection openings, in particular connection openings for delivering and removing fuel and connection openings for sensors and valves and so forth, this object is attained in that the high-pressure fuel reservoir is equipped with a pulsation damping device. By means of the pulsation damping device, the volume of the high-pressure fuel reservoir can be reduced markedly. As a result, the harmonics that occur in operation are damped, and thus the high-pressure strength of the high-pressure fuel reservoir is increased.
A particular embodiment of the invention is characterized in that the pulsation damping device is formed by interference geometries. By means of the interference geometries, the propagation of pressure waves in the high-pressure fuel reservoir is at least hindered. The interference geometries can be embodied in various ways. It is possible for the interference geometries to be formed by separate parts. However, it is also possible for the interference geometries to be embodied integrally with the high-pressure fuel reservoir.
A particular embodiment of the invention is characterized in that the high-pressure fuel reservoir includes a housing with an inner chamber in which the interference geometries are received. The inner chamber can be formed by a bore, for instance. The bore can be embodied as a through bore or as a blind bore. The open end or ends of the bore can be closed with suitable closing elements, to make them high-pressureproof, after the interference geometry is inserted. Alternatively, the inner chamber can be formed by a spherical chamber. In the case of a spherical inner chamber, the insertion of the interference geometries is made possible by a two-part housing.
A further embodiment of the invention is characterized in that the interference geometries are formed by at least one twisted metal sheet, a shaft with pierced transverse walls disposed on it, a wire coil, at least one sheet-metal strip with perforations, and/or a tube with perforations. In designing the interference geometries, care must be taken that the volume of the high-pressure fuel reservoir not be greatly reduced by the interference geometries. In other words, interference geometries that are not/very voluminous are to be preferred.
A further embodiment of the invention is characterized in that the interference geometries protrude through the connection openings or through additional openings from outside into the inner chamber of the housing. The interference geometries can for instance be screwed or welded onto the outside of the high-pressure fuel reservoir. The distribution of interference geometries in the high-pressure fuel reservoir can be regular or irregular, as needed.
A further embodiment of the invention is characterized in that the pulsation damping device is formed by at least one escape piston, which is received, movable back and forth counter to a spring, in the high-pressure fuel reservoir. The escape piston makes active pulsation damping possible. Thus even better results can be obtained than with the passive pulsation damping described above.
A further embodiment of the invention is characterized in that the pulsation damping device is formed by at least one escape piston, which is received, movable back and forth counter to a spring, in at least one bush which is mounted on the high-pressure fuel reservoir. This embodiment offers the advantage that the mounting of the escape piston is simplified. Furthermore, this embodiment can also be employed in conventional high-pressure fuel reservoirs without special changes being made.
A further embodiment of the invention is characterized in that the escape piston is provided with a through hole. The through hole assures that a static pressure equalization can be effected between the regions of the high-pressure fuel reservoir or bush that are separated by the escape piston.
A further embodiment of the invention is characterized in that the side of the through bore toward the spring is equipped with a flow promoter. The flow promoter can for instance be a rounded feature or a countersunk feature. The other side of the through bore can be embodied with sharp edges. As a result, it is attained that the deflection motion of the piston, in the event of a pressure surge occurring in the high-pressure fuel reservoir, takes place counter to the spring.
A further embodiment of the invention is characterized in that the escape piston is prestressed by the spring against a stroke stop. As a result, it is attained that only pressure surges beyond a certain intensity will be damped, as a function of the pressure difference.